Incandescent cathode for electron discharge devices



Patented Feb. 2, 1932 UNITED STATES PATENT OFFICE HANS EWALID RUKOP, 0F BERLIN, GERMANY, ASSIGNOR T0 GESELLSGHAF'I' FT TR DRAHTLOSE TELEGRAPHIE M. B. H., OF BERLIN, GERMANY, A CORPORATION OF GERMANY INCANDESCENT CATHODE FOR ELECTRON DISCHARGE DEVICES No Drawing. Application filed February 26, 1924, Serial No. 695,383, and. in Germany May 30, 1923.

My invention relates to electron emitting cathodes and more particularly to incandescent cathodes for freely emitting electrons, such as are used in the ordinary vacuum tube employed in the radio and other electrical arts.

An object is to provide a cathode which will freely emit electrons at low temperatures so that the necessary electron emission will be obtained at the expense of only a small amount of energy.

Other objects will be apparent from the following description.

Present electric vacuum tubes such as are used for detection, amplification, generation and rectification of electric currents, and for various other uses contain different kinds of incandescent cathodes. One type of cathode is the oxide coated cathode, commonly called the Vehnelt cathode; another type is the pure metal cathode which may be composed of tungsten, tantalum or other metal of high melting point; still another type is the cathode consisting of metal of a high melting point as the basic filament material with additional substances of high electron-emission incorporated therewith, as for instance, tungsten with thorium.

The incandescent cathode according to the present invention belongs with the last type. It consists of a wire of high melting point, as, for instance, tungsten, alloyed with the metal hafnium, which has an atomic weight of 72 or with its chemical combinations respectively. I have found experimentally that the metal hafnium when combined with the usual materials usedas a cathode in electron discharge devices has the property of rendering the resulting cathode free to emit electrons at low temperatures. These additions may be suitably mixed with the original material of the filament before the filament is formed and then Worked up together; however, they may also be added to the finished metal wire as, for instance, by distillation in red heat.

If, after the finishing of the filament, the hafnium is in a strongly oxidized state, it may be advantageously reduced by means of carbon, potassium, sodium, magnesium, or any other suitable reducing agent.

It is advantageous to add to the basic filament material not only hafnium but also small per cents of substances favourable for electron emission, as for instance the metals of the alkaline earths, or the metals of the rare earths as yttrium, scandium, thorium, zirconium, titanium.

It will be obvious to those skilled in the art that my invention is not limited to use in vacuum tubes but may be used anywhere it is desired to employ a high electron emitting electrode.

My invention is not limited to the embodiments described above but I am entitled to any modifications thereof that fairly come within the scope of the following claims:

1. A cathode for electron discharge de vices comprising a metal capable of withstanding high temperatures, halfnium, and the metal of a rare earth.

2. A cathode for electron discharge devices comprising a heat resistant metal, hafnium, hafnium oxide, and the metal of a rare earth.

HANS EWALD, RUKOP. 

